1. Field of the Invention
The present invention relates to an image forming apparatus capable of forming images on opposite sides of a sheet.
2. Description of the Related Art
An image forming apparatus which has a function of performing image forming on opposite sides of a sheet has been widely used. In such a double-sided image forming process of the apparatus, an image is formed on a front side of a sheet, and then image forming on a back side of the sheet is conducted upon reversing back the sheet by a switch back conveyance so that the sheet is reversed back to an image forming section.
The double-sided image forming will be specifically described with reference to FIG. 9. Firstly, a sheet P0 which is accommodated in a sheet-feeding cassette 101 is conveyed to a transferring section 102 through a main conveying passage 100A on an upstream. Then, an image forming processing is applied to a front side of the sheet P0. After that, the sheet P0 is conveyed to a fixing section 103 through an intermediate main conveying passage 100B, and an image is fixed on the sheet P0. Then, the sheet P0 is conveyed to a sheet discharging section 104 having sheet-discharging rollers 104a and 104b through a main conveying passage 100C on a downstream. Until a tailing end of the sheet P0 gets out of a branching lever 105, a part of a leading end of the sheet P0 projects outward from the sheet-discharging rollers 104a and 104b. After that, reverse rotations of the sheet-discharging rollers 104a and 104b perform switching back conveyance to the reversing conveying passage 100D in which the former tailing end is turned as a leading end of the sheet P0. Accordingly, the sheet P0 in a state of being reversed front and back is returned back to the upstream main conveying passage 100A again. Then, the sheet P0 passes through the transferring section 102 and the fixing section 103 so that image forming is performed on the back side of the sheet P0, and the sheet P to which the double-sided printing is performed is discharged to outside from the sheet discharging section 104 (for example, refer to Japanese Patent Unexamined Publication No. 2006-62855).
In the switch-back conveyance, it is necessary that the reverse rotations of the sheet-discharging rollers 104a and 104b makes the leading end (tailing end before switching back) of the sheet P0 assuredly move toward the inlet side of the reversing conveying passage 100D. However, at the time of switching back, there has been a problem that the leading end of the sheet P0 hangs down and is oriented toward the main conveying passage 100B, not the conveying passage 100D, so that the sheet P0 reversely moves to the discharging section 104, and the sheet P0 jammed.